The invention concerns a rotary compressor with enmeshment between a helically geared male rotor and a helically geared female rotor.
The development of rotary screw compressors, i.e. twin-shaft rotary piston machines with distinct helical gear section and diagonal flow through its working space go back to the end of the last century. The basic patent originates from Lysholm, who recognised that an internal compression can be achieved by using helical gearing.
Accordingly, the rotary screw compressor transports the to-be-conveyed medium as a displacement machine with positive conveying not only from the suction side to the pressure side but also compressing it in this manner by reducing the gaps between the teeth. When the armatures or rotors rotate in the housing they disengage at the leading edge on the suction side, so that a cross-section and a volume will be produced for the purpose of suction. During further rotation the rotors become engaged again on their leading edges. The cross-section of the working space which moves along in the axial direction is reduced up to the leading edge on the compression side of the housing, where the compressed medium is pushed out.
Rotary screw compressors can be driven directly by a motor or via a built-in transmission.
Compressors with a high compression ratio (final pressure/suction pressure) over 4.0 are provided with an oil injection in the working space to limit the compression temperature at a maximum of 100.degree. C. In this case, in contrast to compressors without oil injection, no differential transmission is necessary to protect the rotors from contacting each other.
In the case of rotary screw compressors the gap between the end faces of the rotors and the housing should be kept as small as possible to prevent leakage of the compressed medium. The tight sealing gaps necessary for this purpose are achieved by an accurate adjustment of the rotors' position relative to the housing while considering the to-be-expected operating conditions. At the same time, for safety reasons, a somewhat larger gap is chosen than the one required theoretically. However, this safety gap difference increases the extent of the leakage and reduces the efficiency of the compression.
By mounting a gap seal between the rotor spigots and the housing, i.e. directly connected to the working space of the rotors, the amount of leakage can be further reduced, however, this measure has the disadvantage that the distances between mounting have to be increased.
For the purpose of keeping the leakage of environmentally harmful media on the compressor's driven side at a minimum, sophisticated sealing constructions are used.
The rotors of the known rotary screw compressor have spigots provided at both ends, which are mounted in axial and radial bearings.
The strong deflection of the rotors and the simultaneous occurrence of high torsional and bending stresses on the driven rotor spigots is a disadvantage in this construction. To provide the rotors with an as high as possible rigidity and/or to enable to transfer the required torques, the spigots are made as large as possible. Consequently, the bearing diameter and the mounting distance has also to be chosen large.